Simultaneous Improvement of Tensile Strength and Elongation: An Unprecedented Observation in the Case of Hydroxyl Terminated Polybutadiene Polyurethanes

Chemical modifications of hydroxyl terminated polybutadiene (HTPB) with hydrogen bond forming functionalities were used as tactics to improve both tensile strength and elongation of polyurethanes (PUs) simultaneously. PUs were prepared using various diisocyanates with modified HTPB in which dinitrobenzene (DNB) groups are attached to terminal carbon atoms. The spectroscopic studies revealed the presence of an additional hydrogen bonding network between DNB and the urethane backbone which resulted into supramolecular cross-linking and was found to be responsible for significant improvement in mechanical properties of HTPB-DNB-PUs. Also, substantial improvement of elongation at break was observed in the case of HTPB-DNB-PUs. Small angle X-ray scattering (SAXS) and thermodynamical studies indicated a strong segmental mixing between the hard and soft segments of HTPB-DNB-PUs. Growth of partial crystalline character in HTPB-DNB-PUs was believed to be responsible for “fibrous-assembly” morphology. In summary, modification of HTPB induced extra cross-linking through supramolecular hydrogen bonding which in turn concurrently enhanced both strength and elongation of PUs.